The truce, agreed between America and Russia, only came into force yesterday Credit: Reuters

Saudi Arabia has accused Russia and the Syrian government of violating the ceasefire which only came into force one day ago.

Speaking at a news conference in the Saudi capital Riyadh, Foreign Minister Adel al-Jubeir claims the respective air forces violated the cessation of hostilities.

He warned there would be a "plan B" if it became clear that Syrian President Bashar al-Assad's government and its allies were not serious about the truce.

"There are breaches of the truce by the Russian air force and the regime and we are now consulting on this matter with the countries of Syria's support group, and I think that the commitment to the truce will be an important indicator of the seriousness of the Syrian regime," Mr Jubeir said.

Danish Foreign Minister Kristian Jensen, also speaking at the conference, called for a "strong alliance" to put military pressure on the Assad regime to help end the war in Syria.